Bleaching agents and conditions for bleaching extracted soybean oil gums under ordinary pressure have been studied.
By removing the aqueous phase separated after bleaching, the use of sodium chlorite and phosphoric acid as a bleaching-aid was effective for lowering the water content of gum and for reducing the amount of bleaching agent remaining in the treated gum.
The amount of necessary bleaching agent actually consumed in the bleaching was very little, however, a large excess of bleaching agent was necessary and “Aging” process was also necessary in order to achieve a good bleaching effect. Use of hydrogen peroxide concurrently with benzoyl peroxide was also proved to be effective.
In the preparation of paste lecithin, bleaching and simultanous drying could be achieved by adding the bleaching agent to the gum and by subsequent evaporation under vacuum.
Sodium chlorite with acetic acid, phosphoric acid or citric acid as a bleaching-aid was proved effective. In this case, simultaneous use of hydrogen peroxide and benzoyl peroxide gave a better result. This was ascribed to the preferential bleaching function of these bleaching agents for different coloring substances in the gum, from the result of spectrophotometric analysis of the gums before and after bleaching.